Windows x64 went beta in 2003 and I started using it in 2004 and, yes, performance for some things were better but there were some headaches using it as well - particularly drivers. It took quite a few years before x64 became mainstream or even where it wasn't a small percentage of Windows sales.
What percentage of Windows programs are running in 64-bit mode today where the 64-bit OS is mainstream? I can tell you that Firefox runs in 32-bit mode. They have a 64-bit version but it perennially in development. I built working 64-bit Firefox browsers back around 2005 or 2006 (they're still downloadable from my website) but we still don't have a shipping product today.
Apple's 64-bit iPhone 5S launch went pretty well but customers experienced various crashing problems attributed to their 64-bit operating system. I'm fairly happy with my iPhone 5 which is only 32-bit. Same thing with my Nexus 7. My wife is happy with her Nexus 5 which is 32-bit with a Snapdragon 800 which really smokes.
64-bit is perception. 64-bit programs use up more storage (flash and RAM) while very few applications need it. The only applications where 64-bit addressing is helpful for me are video editing and virtual machines. My home desktop can hold 24 GB of RAM (there's somewhere between 9 and 13 GB on it) but I seldom go above five and that's with a VM. If I'm not running a VM, then I usually run less than 3 GB.
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